The FBI says it still has not made any arrests after searching a downtown Spokane apartment as part of an investigation into the discovery of a pair of letters containing the deadly poison ricin.

The letters were postmarked last Tuesday in Spokane and addressed to the downtown post office and the adjacent federal building.

Few details have been released, but investigators in hazmat suits spent from 7 a.m. to 10:30 p.m. Saturday executing a search warrant at a three-story apartment building. Authorities said there was no public health risk.

The Spokane investigation comes a month after letters containing ricin were addressed to President Barack Obama, a U.S. senator and a Mississippi judge. A Mississippi man has been arrested in that case.